Cellular synthetic fibre thread and a method of making the same



Dec. 10, 1957 Filed Aug. 3, 1953 CELLULAR S YNTHETIC FIBRE THREAD AND N. ROBINSON A METHOD OF MAKING THE SAME 5 Sheets-Sheet 1 Rowland. N. Robinson @6 f wray Dec. 10, 1957 R N. ROBINSON 2,815,559

CELLULAR SYNTHETIC FIBRE THREAD AND A METHOD OF MAKING THE SAME Filed Aug. 3, 1953 3 Sheets-Sheet 2 IN V EN TOR.

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W A ORNEY Dec. 10, 1957 R. N. ROBINSON 2,815,559 CELLULAR SYNTHETIC FIBRE THREAD AND H A METHOD OF MAKING THE SAME Filed Aug. 3, 1953 3 Sheets-Sheet 3 mson United States Patent Ofiice 2,815,559 Patented Dec. 10, 1957 CELLULAR SYNTHETIC FIBRE THREAD AND A METHOD OF MAKING THE SAME Rowland N. Robinson, Worcester, Mass., assignor to The Robinson Thread Company, Worcester, Mass., a corporation of Massachusetts Application August 3, 1953, Serial No. 371,934 3 Claims. (Cl. 28-74) This invention relates to synthetic fibre thread and a method of making the same, and more particularly to the production of threads and yarns made from synthetic fibres which may be exposed at least momentarily to detrimental temperature conditions.

Various types of synthetic fibre thread and yarn are made from synthetic polymeric fibres, such as the linear polyamide resins, acrylic resins, polyester resins, vinyl resins and copolymers thereof, and including cellulose acetate, viscose, cuprammonium and protein fibres. Many of these various materials are thermoplastic or have melting or degrading points at less than 500 F. so that their use is limited to applications that will not expose the thread materially to higher temperatures. These polymeric fibres are individually shaped as filaments or fine rod-like bodies and they are highly dense or non-porous and readily conduct and absorb heat. On the other hand, the natural fibres, such as cotton, linen and wool, although they will deteriorate under high heat, nevertheless contain minute air cells which provide a certain measure of heat insulation. These natural fibres are not straight or rod-like but are naturally bent and crinkly or curly, so that when placed together to form a yarn or thread they do not lie in tight contact or parallel formation one with another. The helter-skelter arrangement of these fibres and the consequent air spaces therebetween makes such threads capable of resisting high temperatures for a much longer period of time than will a synthetic rod-like fibre. On the other hand, the synthetic or polymeric fibres have the strength, elasticity and other desirable qualities which render them particularly useful for sewing threads as well as for weaving various types of fabrics. Yet an inability to resist temperatures often required in their use detracts materially from their utility. For example, when yarns made of nylon are woven into fabrics, the material should not be ironed at a normal flat-iron temperature of 500 F., for the fabric would melt or deteriorate. A cotton fabric, however, may be safely ironed at this temperature because of the slower penetration of the heat. As a further example, when a sewing thread is run at high speed under standard commercial usage, the needle will become heated through friction and the temperature may sometimes rise as high as 800 or 900 F. The cotton thread will pass safely through such a hot needle, but the synthetic threads will absorb the heat more rapidly and may be melted or weakened in their strength to the point of breakage.

Nylon thread is formed as a condensation product of adipic acid and hexamethylene diamine. This compound is extruded from a molten condition under the influence of heat and pressure as very fine filaments. For use as a thread or yarn, a plurality of these filaments are grouped together and usually with a slight twist to hold them in place. The high degree of elasticity of the compound is reduced and the thread is stabilized by subjecting it to a high temperature under tension which thus causes the twist to become set and limit the ultimate stretchability of the thread. However, the material has a melting point of 482 F. and since the nylon filaments are present in a closely packed or dense condition in the thread, the heat conductivity of the material is high and so presents the problem above explained. Similar difiiculties are faced in the use of the other types of synthetic thread polymers, such as acrylonitrile fibre or a polyester fibre made by condensing ethylene glycol and terephthalic acid, as well as the various vinyl polymers and others included under the general term of synthetic thermoplastic polymeric thread fibres or filaments, herein classed as fibres.

It is accordingly the primary object of my invention to overcome such problems and to provide threads or yarns, herein termed threads, made of synthetic thermoplastic polymeric fibres which will resist the momentary application of heat normally higher than the fusing or degrading point of the material at which the thread material is unstable and detrimentally affected, such as when a thread is passed through a highly heated needle or when the fabric woven therefrom is momentarily subjected to a high temperature.

A further object of this invention is to provide a method of rendering synthetic thermoplastic polymeric threads more highly heat resistant.

In accordance with my invention, I propose to incor porate air cells within a thread made of a multiplicity of synthetic thermoplastic polymeric fibres, so as to provide heat insulation within the structure and enable the thread to resist the momentary application of a high temperature.

A further object therefore is to provide a method of so treating a thread of synthetic substances as to give it an air filled cellular structure having a substantially smooth surface and yet retain its strength and other desirable properties even when the thread is subjected to the tensions and temperatures involved in standard uses, such as sewing and weaving.

Still further objects are to provide a method whereby such an air filled product may be made economically; simply and efiiciently and desirable and beneficial properties are imparted to the thread. Other objects will be apparent in the following disclosure.

Referring to the drawings illustrating various aspects of this invention:

Fig. l is an enlarged photograph of a thread made of the substantially parallel filaments of a nylon polyamide compound;

Fig. 2 is a similar enlarged photograph of such a thread when crinkled and expanded to provide air spaces within the structure;

Fig. 3 is a similar photograph of the material of Fig. 2 after it has been impregnated with a thermoplastic resin material which stabilizes the cellular structure;

Fig. 4 is a view similar to Fig. 3 of the thread after it has been coated and air cells stabilized therein;

Fig. 5 is a diagrammatic, longitudinal section through the coated thread;

Fig. 6 is a diagrammatic view of an apparatus capable of carrying out the process of providing the thread with included air cells;

Fig. 7 is an enlarged fragmentary view of the fibre crinkling apparatus; and

Fig. 8 is a fragmentary detail of mechanism for rolling the thread on the coating roll, the view being taken on the line 8-8 of Fig. 6.

Although the process is applicable to various synthetic thermoplastic polymeric substances, suchas herein specified, the invention will be explained and illustrated with reference to the production of an air filled polyamide thread. As is well known, a standard nylonthread is made up of a multiplicity of substantially parallel filaments of very fine size which are smooth surfaced and rod-like in structure, as made by extrusion of a condensation product of adipic acid and hexamethylene diamine. These filaments are set in a slightly twisted condition to prevent the thread filaments from separating and to resist undue elongation under tension. Such a thread is shown in the enlarged photograph of Fig. 1. In accordance with my process, I separate those filaments and render them crinkled and wavy, and so provide a loose, highly porous structure, as illustrated in Fig. 2. If that structure of Fig. 2 were subjected to heat while under tension, it would tend torevert to the non-crinkled rodlike structure of Fig. 1. I, however, stabilize that crinkled condition and set the crinkled structure with its highly developed cellular nature and filled with air cells. This deprives the thread of its former high elasticity and prevents the fibres from returning to their original straight or rod-like shape, and particularly during subsequent heat treatments. I may also coat the exposed surfaces of the thread fibres with a coating which holds air cells therein and gives the thread a smoother surface and desired qualities for use in sewing and weaving.

To this end, I cause the crinkled intermeshed fibres to adherefin an expanded cellular structure. This may be done by incorporating in the pore spaces and interstices between the individual crinkled and intermeshed fibres a suitable fluid adhesive or a plasticizer for the thread fibre, which is capable of causing the fibres to adhere, and of heat hardening the adhesive sufiiciently to hold the fibres in a desired spaced or cellular condition, as shown in Fig. 3. The adhesive, such as a plasticizer or a cement, is used only in a limited amount, ordinarily not over 25% by weight of the thread, but sufficient to'coat the filaments adequately for cohering in the expanded air filled cellular or sponge-like arrangement and not fill a high percentage of the spaces, so as to leave the body in a heat resistant condition because of the contained air. The adhesive is present as a bond between the fibres and serves as struts between and spacing the fibres and forming Walls defining and sealing in some air cells. Although not always required, the outer surfaces of the impregnated mass of stabilized crinkled fibres may also be coated thereafter with a suitable coating compound, such as a synthetic resin, which forms substantially a shell around the, air cell structure and aids in stabilizing the air cells in; a. porous structure. The coated thread is shown; in the photograph of Fig. 4 and diagrammatically in Fig. 5. Such a thread may also be made of short staple fibres which have been crimped or precrinkledand then spun into a yarn, and wherein the air cells in such a structure are likewise stabilized, and itis to be understood that this invention applies to a thread made either of long or continuous filaments as well as the shorter precrinkled staple that has been spun into a suitable thread structure.

As shown diagrammatically in thediagrammatic sketch of Fig. 5, the thread in its final form comprises a'plurality of crinkled fibres 1 of the desired synthetic polymeric resin; These fibres are secured together at contiguous or adjacent points by suitable treatment so as to provide a substantially permanent air filled cellular structure. This is preferably accomplished by impregnating the expanded structure With sufiicient plastic cement to afiix the fibres at contiguous or adjacent. points and thereafter heat setting this cement. Since air spaces are to'be retained in the thread, it is preferred'that the cement be used in only a small amount but sufiicient to effect the cohesion of the fibres. This cement 2 is indicated diagrammatically in Fig. as forming bonds and struts between the crinkled fibres which secures them together in an open or porous air filled structure and wherein these bonding posts may occupy only a comparatively small portion of the cellular space 3, and preferably not over 50% of the volume of the final product. These air cells are intended primarily for heat resistance and it is desirable to retain a substantial proportion of the air in the thread, although the thread may be drawn down to a much smaller diameter in later steps in the process. Although the thread may be used in the form of Fig. 3 for many types of operation; it is preferred to coat the thread with a coating material, such as'a thermoplastic or thermosettable resin, which seals in many of the air cells and at the same time provides a much smoother surface, which may be considered as substantially cylindrical; to aid in its slipping readily through a needle or in weaving operations. The thickness of this coating 4 will depend upon the intended use for the thread, but ordinarily it is sutficient to seal a considerable and preferably the major portion of the air pores at the surface of the thread.

Assuming that the thread is initially composed of long rod-like polyamide filaments of suitable size made in accordance with standardpractice, which has the general appearance shown in Fig. 1, this thread may be given a crinkled structure by various standard procedures, such as by highly twisting the filaments and setting the same in that twisted, wavy or curled condition, as by the application of heat, after which the thread is twisted in the opposite direction in the attempt to remove the twist but which causes the filaments in their now set and wavy or curled condition to separate into a highly crimped structure of the general nature shown enlarged in Fig. 2 of the drawings. A suitable apparatus for carrying out this stage of the process is shown diagrammatically at the lower left corner of Fig. 6 and in enlarged detail in Fig. 7. p

The nylon thread 10 derived from a suitable source, shown in Figs. 6 and 7 as a bobbin 11, is passed between driven rolls 12 and thence through an oven 14 to a twisting apparatus 15. The twister comprises a shaft 16 drilled axially to provide the passage 17 through which the thread travels to a wind-up bobbin 18 suitably driven at a speed coordinated with that of the rolls 12 to provide the proper tension. As shown in Fig. 7, the central passage through the shaft 16 terminates in two openings 19 in the rotating shaft 16,v each arranged at an oblique angle to the shaft axis. A cap 20 removably threaded on and spacedfrom each end of the shaft 16 has a central opening 21 which is in alignment with the axial passage 17. The cap is spaced from the slanting opening 19 to provide space. for a loop of thread between the openings 17 and 21. The shaft is driven by a suitable motor 23 and belt connection 24 with a pulley 25 secured to the shaft. It will thus be seen that the oblique passage 19 at the right hand end of thetwisting apparatus 15 serves as a crank arm to form a' first twisting head and twist in one direction the portion 26' of the thread between the nip'rolls 12 and the first passage 19. That is, the first twist extends back through the oven 14 to the rolls 12. The oven 14 through which the twistedthread passes is hcated'by hot air from a suitable gas or other burner 27. The hot gases are blown by the blower 28 into the space 32 within the oven and thence circulated through holes in the partition 33 into contact with the twisted thread body 26. The heated gases pass outwardly through the exit pipe 34.

It will be appreciated that the thread has a uniform twist between the nip rolls 12 (Fig. 7) and the first or right hand twisting head at 19. The temperature in the oven 14 is maintained at a point below the melting point of the thread but high enough to set the thread in its twisted condition, sucha's about 325 F. for a polyamide filament or an acrylonitrile fibre, which is capable of the thread passes outwardly through a second twisting head passage19 (Fig. 7) at the left hand end of the apparatus 15', which rotates in the same angular direction as does the twisting head passage 19 at the right hand side. The second twisting head at the left is shaped the same as the first twisting head at the right hand end of the shaft 16. It attempts to remove the twist that has been imparted to the thread by the first twisting head in the oven 14, but the first twist has been fixed by the heat setting step in the oven, so that the second left hand twisting head cannot untwist the set condition but serves only to loosen the fibres and leave them in a crinkled and wavy condition, which is illustrated generally in the photograph of Fig. 2. Thus the thread is opened up into a cellular body having a very considerable-air mass and which has a diameter several times that of the initial straight filament thread, as shown in the photograph of Fig. 2, it being noted that these photographs of Figs. 1 to 4 are made with the same magnification.

The next stage of the process comprises setting the expanded crinkled structure of Fig. 2 in the condition of Fig. 3 which maintains air spaces in a thread of a suitable diameter. To this end, the thread of Fig. 2 is progressively and suitably pulled out longitudinally, such as to about one-half of its diameter, and the body of the thread is treated in a bath of a suitable plastic adhesive, such as a thermoplastic or heat settable resin solution, to coat the individual fibres or filaments with enough adhesive to cause the filaments or fibres to stick together at various points and particularly where they are close or come into contact. As shown in Fig. 6, the crinkled thread is led from a bobbin 30 through a fluid adhesive bath in the container 32 where enough adhesive is applied to the crinkled fibres of the thread to coat them at contiguous points and cause the cohesion of the fibres. This apparatus comprises a pair of rolls 34 so arranged that the crinkled thread 35, derived from the above described operation or otherwise, passes over the upper roll and between the rolls and then around the lower roll to another pair of rolls 36 as shown, where the thread passes between the rolls and thence upwardly into a heating apparatus arranged to thermally set or harden the plastic adhesive and secure the crinkled fibres together. The lower rolls of each pair are suitably driven, as by chain or gear drives from a constant speed electric motor, and the upper rolls of each pair are weighted idlers. The second pair of rolls 36 serves to remove exces plastic from the thread and thus to insure that air cells will remain in the cells between the intermeshed fibres. It is ordinarily desirable that at least 50% of the cell spaces in the thread remain unfilled.

After the thread has been sufficiently impregnated with the plastic or cementing material to cement together the contiguous fibre or filament portions, the impregnated thread 40 is passed progressively through a heating zone where the cement is set in a hardened or a permanent condition by means of heat. The heating apparatus comprises outer rectangular casing walls 42 defining an enclosure through which heated air derived from a suitable heat generator 43 is transported by means of a blower 44 and a conducting pipe 45 into a centrally located vertical pipe formed by vertical spaced parallel walls 46 and 4'7 extendin lengthwise between they end walls of the casing. The inner space between the walls 46 and 47 opens at the top into an enclosed chamber beneath a partition 48 arranged to direct the hot air downwardly as indicated by the arrow into a passage outside of wall 46 formed by a partition 49 parallel to wall 46. The hot air passes to the bottom of the casing and then upwardly in another passage formed by a wall of casing 42 and an inner wall 50 parallel thereto. The wall 50 is spaced from wall as to provide a passage through which the thread body 4% passes upwardly. The hot air in the passage outside of wall 50 returns to the heater 43 through the upper conduit 51. Various supply pipes and dampers may be employed with this apparatus to control the quantity and pressure of the heated air, and a suitable thermostat control provides a controlled temperature, such as about 300 F., for a polyamide or an acrylic fibre.

The thread 40 that has been impregnated in the bath 32 passes vertically upwardly through a suitable opening in the bottom of the heating apparatus 42 and into the space between the walls 49 and 50. The thread is drawn upwardly by a driven roll 52 above the casing 42. While traveling upwardly, the thread is subjected to high speed jets of heated air issuing under pressure from the jet pipes 54 which project from the walls 49 and 50 directly toward the upwardly passing thread. The air pressure of the jets is provided by proper control of the blower 44 and it is such that the jets serve to agitate the filaments or fibres of the traveling thread and to break up close adhesions and cause the thread to assume a satisfactory cellular condition prior to the plastic cement becoming hardened.

Although the drawings show the progress of only a single thread, it is more economical and practical to pass a considerable number of the threads in parallelism through the various stages of the impregnating, coating and heat treating apparatus. The nozzles 54 are accordingly so shaped and directed that the heated air will strike directly against each thread and the impact will loosen the fibres, subject of course to the restraint imposed by the tension that has been applied to the thread. The primary loosening effect on the cellular structure is accomplished by the lower jets of the series, since the temperature of the air in the jets is maintained at a point at which the plastic resin or cement is set or hardened by the time it has reached the top of the heating apparatus. This stage of the process therefore accomplishes the cementing together of the various fibres of the thread in their cellular and spaced condition. The diameter of the thread and the residual air spaces and adhesions at this point are controlled by adjusting the speeds of the driving rolls 36 and 52, taking into account the thread size, its shrinkage under heat and the amount of resin or adhesive applied by the bath 32. For example, the coated thread may be pulled out to a diameter which is approximately one-half of that of the cellular thread on the bobbin 30 prior to its passing to the lower coating bath 32. This is indicated by a comparison of sizes in Figs. 2 and 3 of the drawings. The structure of the impregnated thread is shown in Fig. 3, it being evident that pore spaces are retained in the thread and that the thread body does not in any way resemble the original thread of Fig. 1 with its multiplicity of substantially parallel filaments.

Since the thread i to be used in sewing and other operations which require a reasonably smooth surface on the outside of the thread, and it is desirable that air cells be retained permanently within the thread body, I prefer to coat the plastic impregnated and cemented fibre thread with a further material which holds air cells therein and forms a reasonably smooth or slippery coating. This is preferably accomplished by applying a suitable adhesive, such as a solution of a resin, to the upper driven roll 52 and passing the cemented fibre over the roll. The roll is coated with a suitable resin or other solution or plastic supplied by a bath 60. The roll 52, or a supplemental contacting roll, not shown, dips in the liquid resin of the bath 60 and thus provides a liquid coating on its surface, which is to be transferred to the outer exposed surfaces of the cemented thread body 40.

One suitable way of securing an even coating is to roll the traveling thread back and forth through a suitable distance across the plastic coated smooth surface of the cylindrical steel roll 52 and thus cause the thread to. pick up a coating throughout its entire circumference. This rolling action insures that the plastic coating is ap plied primarily to the outer thread surface and quite uni formly. 'Various types of apparatus may be employed-f for this purpose, such as that shown in'Figs. 6 and 8.. This comprises a pair of fingers 62 spaced on opposite:

sides .ofeach threadand arranged to reciprocate laterally and carry the thread over the roll surface. To this end, the series of fingers 62may be mounted on a suitable slide :bar 63 carried on a'support 64, such as by means of .adovetailed slideway therebetween. The slide bar 63 hasaidepending cam follower 65 which is slidably iountedIin thecam groove 66 of a suitable barrel cam 67 that is driven by suitable electric motor or other drive connectionat arate which causes each thread to roll through at least one revolution as it is being drawn steadily over the driven roll 52 which has the plastic coating. The coated thread body 70 passes between a pair of suitable driving rolls 72, thelower of which is driven at a speed coordinated with that of the other rolls. The upper roll is .preferably a weighted idler which bears against the thread .and maintains it properly positioned. If desired, the driven roll 72 and the coating roll 52 and associated parts may -be interchanged in position, so that the coated thread body at 70 will not contact any further rolls until after the coating has been heat hardened.

After the coating has been applied to the thread, the coated portion 70 of the thread is passed downwardly through a suitable opening in the top of the heating apparatus 42 }into another heating zone, as shown at the right hand side of Fig. 6. This zone is formed by two parallel spaced walls 74 and 75 spaced between the wall 47 and the outer casing wall 42. The space between walls 47 and 74 forms a down draft passage through which part of the hot air in the central updraft passage 46, 47 returns to the bottom of the casing. The heated air is then conducted upwardly in the outside passage and returns to the heater and blower, as indicated by the arrows. The walls 74 and 75 are provided with large openings 79 arranged between bafiles 80 which direct the air and provide for a fiow of the heated air into the space between walls 74 and 75 and around the coated thread body 70. The moving air currents do not disturb the coating on the thread, and as the thread travels downwardly, the resin coating is gradually hardened and some air cells inside of the thread are sealed in place. The thread is drawn downwardly under a suitable tension by means of a pair of driven rolls 82 from which it is transported to a suitably driven wind-up bobbin 84. At this stage of the process the thread has the general appearance of that in Fig. 4, it being noted that the thread may be slightly twisted although it has a substantially cylindrical exterior within the general requirements of a thread that is .used in sewing or weaving.

The various sets of rolls above mentioned are suitably driven at required rates by interconnected driving mechanism or by separate constant speed motors. The adjustment of speedmay be accomplished by speed changing devices or merely by a choice of interconnected gears of suitable sizes. The speeds at which the various rolls are driven are related to the thread size and to the amount of cement or plastic resin applied, as well as the nature of the thread material. It is required to maintain satisfactory tension on the thread all stages which insures a proper run of the thread. Different types of thread substance act differently under tension and heat and the speed is governed accordingly. If, for example, an acrylic fibre of 400 denier is being treated by impregnation in bath 32 with about 8% by weight of a polyamide resin, the thread may be run at 25 feet per minute through the bath 32 and upwardly into the heating zone between the air jets 54 where it is subjected to the blast of hot air at a temperature of about 300 F. The temperature of the air, the rate of drive of the thread and the thread denier" are related, since the hot air jets must blow out or open up the cellular or sponge-like structure in the thread to a desired extent before the cementing resin has hardened. For the above-mentioned impregnation of 8%, which is satisfactory for one type of thread, an acrylic fibre thread of 100 denier may be run at about feet per minute. A heavier application of resin would require a slower driving rate.

The rolls 34 and 36 are driven at substantially the same rate, while the roll 52 is driven at a sufiiciently faster rate to cause the thread to be elongated and its thread diameter reduced to about /2 that of the coated body in the bath 32. Likewise, the lower roll 82 and the wind-up bobbin 84 are driven at such a rate relative to the upper roll 72 as to pull out the coated thread body 70 to provide a desired reduction of diameter. For example, the finished coated thread may have a diameter of about /2 that of the heat set portion 40 of the thread body prior to the last coating stage at roll 52. To this end, the roll 82 may be driven 10% faster than the roll 72 of the same diameter, and the roll 72 may be driven 5% faster peripherally than the roll 36. This difference in speed takes into consideration the fact that in its upper run from roll 36 to roll 52 a crimped thread without a coating tends to 'shrivel under heat, and this action takes place to a certain extent in the impregnated body. During the original crimping step, the crimping is accentuated and afterwards it is partially released so that the thread tends to go back to the desired degree of crimp.

It will now be appreciated that various types of impregnated and coating materials may be employed and that their temperature, plasticity and adhesiveness may be suitably controlled. The crinkled thread fibres may be caused to adhere at contiguous or adjacent points by various procedures, such as are standard in the synthetic resin industry. For example, the fibres in the expanded and crinkled condition of Fig. 2 may be cemented together adequately by dipping the thread progressively in a solution of a substance capable of both adhering to the thread fibre and of being hardened by heat under the conditions of the process. One suitable cement of general purpose for partially impregnating and cementing together many of the synthetic polymeric fibre substances may be formed by making an emulsion of parts by weight of dibutyl phthlate with 1.25 parts of oleic acid, 0.35 part of ammonium hydroxide and the balance of water. I may use 30 parts by weight of this emulsion as a plasticizer for parts of vinyl acetate. The prodnot is a liquid plastic material which may be used at room temperature or higher but preferably below about 160 F. in accordance with the degree of partial thread penetration required and the quantity that is to adhere to the thread fibres.

Another suitable cement is formed of diethylene glycol mixed with adipic acid, with about 10% excess of the glycol. This mixture is heated for about 4 hours at 425 to 450 F. and then dissolved in about 10 parts of ammonia in parts of water; and 30 parts of this solution are added to 70 parts of a polyvinyl acetate emulsion. An adhesive which is useful for nylon fibres is made of diethylene glycol or glycerine and polyvinyl alcohol. The alcohol is formed by hydrolyzing polyvinyl acetate, and a solution in water containing from 10% to 20% of the alcohol is combined with 10 to 20 parts by weight of glycerine or diethylene glycol. The adhesive thus formed adheres to the nylon and particularly at contact points of the crinkled intermeshed fibres. The heat treatment above specified, such as subjecting the impregnated or coated thread to a temperature of 300 F. for a short period of time, serves to heat set the cement in its bonding relationship. Various other thermoplastic or thermosetting adhesives may be adopted for cementing the polymeric resin and other fibres, and the temperature of the bath, viscosity and length of time of the treatment may be widely varied to control the extent of the bonding action.

It will also be appreciated that the air filled, crinkled and intermeshed fibre structure may be immobilized to a required extent by causing the thread fibres to adhere directly to one another, as by means of a suitable plasticizer capable of softening the fibre surface sufiiciently to permit the cohesion. For example, theouter surface of nylon polyamide fibres may be sufiiciently plasticized by so treating the nylon substance as to form a methoxymethylated 66 nylon substance. A solution of methyl alcohol and formaldehyde in an 80% formic acid solution in water may be employed, in which the nylon thread is passed through that solution for a brief period of time to soften the nylon fibres enough to render them tacky at their surfaces. The thread may be dried at about 115 C. The time of contact of the nylon with the solution and the temperature may be widely varied in accordance with the degree of cohesion desired. Also, nylon thread may be dipped in other suitable solvents, such as 80 parts of ethanol in 20 parts of Water, which softens the nylon surface. Other resin fibres are readily rendered tacky or sticky on their surfaces by means of solvents which are appropriate for the particular thread being used. For example, the Orlon acrylic fibre may have its surface rendered slightly plastic by means of a dimethyl formamide solvent.

The coating applied by the roll 52 on the outside surfaces of the expanded thread structure may be any desired thermoplastic or thermosettable polymeric resin substance, such as those which form the filament or thread fibre, or it may be formed of special cement solutions or plastics, such as those used in the bath employed for initially impregnating the crinkled and intermeshed thread fibres. The coating and impregnating substance may be selected from the class consisting of linear polyamide resins, acrylic resins, polyester resins, vinyl resins, polystyrene resins, coumarone resins, melamine formaldehyde resins, furan resins and copolymers thereof. For example, the thread may be coated with a resin derived from ethylene glycol and terephthalic acid and methyl phthalyl ethyl glycolate. An emulsion of 15 parts of the resin in water may be applied satisfactorily to a thread formed of Orlon polyacrylonitrile resin. A solution of a nylon polyamide resin of the type known as 8-8 nylon in aqueous ethyl alcohol and having a concentration of about 10% of the resin will serve for coating a Dacron polymeric resin formed of polyethylene glycol terephthalate. Nylon thread may be coated with an emulsion of polyvinyl chloride in polybutyl benzyl phthalate in which the total solids forms 20% of the emulsion. Nylon thread may also be coated with an aqueous dispersion of polystyrene resin and diethyl phthalate having a total solids content of about 38%. Similarly, melamine formaldehyde resin may be emulsified with a plasticizer formed of toluene sulfonamide and used as a coating.

Various solvents may be employed to dissolve the substance of the chosen resin and to form a plastic bath of suitable viscosity for the coating operation, such as by dissolving a nylon resin in a solution of 80 parts of ethanol and 20 parts of water. The coating may be formed of materials different from that of the thread substance. For example, a water emulsion of polystyrene with diethyl phthalate containing 40% of solids may be applied to coat a nylon thread. Likewise, the polyacrylonitrile may be coated with a material formed by dissolving 1 part of a nylon polyamide in 8 parts of ethyl alcohol containing 0.3 parts of dibutyl phthalate. The specified ccating materials are water insoluble and permanent thermoset polymeric resins which form a smooth surfaced thread having heat resistant air sealed within the spaces between the crinkled fibres. The temperature and viscosity of the coating bath is suitably regulated to insure a desired thickness of coating on the thread. This coating, however, should be comparatively thin so as not to increase the thread size materially and yet provide the desired smoothness of surface. Because of this thinness of coating on the exterior surfaces of the outer fibres, it is found that various fibres may stick out from the side of the thread and provide a thread-like appearance.

It will be appreciated this invention applies to a precrinkled thread, such as a spun yarn made of short precrinkled fibres spun into a thread or yarn or acornmercial precrinkled thread of long filaments twisted together, as well as to a thread made in one progressive process by crinkling a thread of a multiplicity of rod-like filaments and then cementing the expanded air filled body as above described. Also, there is no precise limit to the pore volume of the thread, since this may be varied according to the intended use of the thread, yet ordinarily I prefer to have at least 10% of the thread volume occupied by air filled pores and for many purposes the air cells ap preach or exceed 50% of the volume. These cells or pores are in part open to the exterior and in part sealed in by the inner cement or the outer coating, but the reinforcing formed by the cement struts and coatings insures that the cells or pores will remain under normal usage and provide heat resistant air Within the thread body.

The thread herein described may be considered as having an immobilized cellular structure, although the thread fibres are fully mobile in bending and stretching in an ordinary thread manner, but the immobilization applies to the cell structure in that the cells or pores are substantially permanent like the structure of a sponge and will provide air spaces under normal conditions. The cementitious material employed to immobilize the cellular structure may be formed by a solvent which renders contiguous portions of the fibres tacky and cohesive or by an added cement, preferably a thermoplastic or a thermosettable resin type of substance, which becomes a permanent part of the thread structure. The various materials may be either thermoplastic or of a type which sets irreversibly under heat, but insofar as this invention is concerned, these various materials may be considered as thermosettable because of their being hardened by heat to a condition which is permanent for ordinary thread usage.

I claim:

1. A synthetic fibre thread comprising a flexible ex panded body of a multiplicity of intermeshed crinkled fibres of a multiple filament thermoset synthetic polymeric thread substance, a cementitious material permanently uniting adjacent portions of the precrinkled fibres in said expanded body' and forming an immobilized cellular structure of a predetermined elongation, and a permanent, water insoluble, thermoset polymeric resin coating adhering mainly to the exterior fibres and forming a smooth, continuous outer shell which provides for the thread slipping readily through a needles eye, said thread having at least 10% by volume of scaled internal space filled with air and being heat resistant momentarily to a temperature at which the thread substance is detrimentally affected in sewing and ironing operations.

2. The method of making a flexible synthetic fibre thread comprising the steps of heat softening and crinkling the fibres of a multiple filament synthetic thermoplastic polymeric thread, hardening the crinkled fibres and forming an expanded cellular structure of a definite elongation, cementing together adjacent portions of the thread fibres and forming a flexible immobilized cellular structure having at least 10% by volume of air filled cell space, applying a coating to the exterior fibres and thr -d surfaces of a heat resistant thermosetting polymeric ream, and thermoset-ting the coating to form a permanent shell of a thickness which seals exterior cellular spaces and provides a substantially continuous smooth surface entrapping air in the interior and thereby forming a high speed sewing thread which is resistant momentarily to high temperature at which the thread substance would be detriment-ally affected.

3. The method or" making a synthetic fi'bre thread comprising the steps of progressively heating and crinkling the fibres of a multiple filament thermoplastic polymeric thread, hardening the crinkles and progressively expanding the crinkled thread body to form an intermeshed non-adherent air filled crinkled structure, progressively impregnating the air filled thread body partially with sulficient thermoplastic polymeric resin substance to cause adhesion of adjacent fibre portions, subjecting the thread progressively to a hot air jet to reduce a'dh-esions within and expand the thread, tensioning and elongating the thread materially to a predetermined length, heat setting the cement and forming a permanently expanded air filled cellular structure, progressively coating chiefly the exterior surfaces of the thread with a polymeric resin and forming a smooth substantially non-porous coating of limited depth which seals air spaces of the inner cell structure, and progressively heating and thermosetting the coating while maintaining the thread under tension and controlling the thread length and diameter.

References Cited in the file of this patent UNITED STATES PATENTS Alibert Apr. 13, 1937 Davis et al. Oct. 22, 1940 Wallaeh Aug. 19, 1941 Bloch Apr. 5, 1949 FOREIGN PATENTS Great Britain Oct. 5, 1936 

2. THE METHOD OF MAKING A FLEXIBLE SYNTHETIC FIBRE THREAD COMPRISING THE STEPS OF HEAT SOFTENING AND CRINKLING THE FIBRES OF A MULTIPLE FILAMENT SYNTHETIC THERMOPLASTIC POLYMERIC THREAD, HARDENING THE CRINKLED FIBRES AND FORMING AN EXPANDED CELLULAR STRUCTURE OF A DEFINITE ELONGATION CEMENTING TOGETHER ADJACENT PORTIONS OF THE THREAD FIBERS AND FORMING A FLEXIBLE IMMOBILIZED CELLULAR STRUCTURE HAVING AT LEAST 10% BY VOLUME OF AIR FILLED CELL SPACE APPLYING A COATING TO THE EXTERIOR FIBRES AND THREAD 